Season the pork by lightly coating the meat with truffle salt and pepper, then layer on the djion mustard. Half, pit, then quarter the plums. In a deep bowl, sandwich the tenderloin between two layers of plums and marinate for an hour. In a large saute pan over high heat sear only the tenderloin until brown on all sides. Lower the heat to a simmer, add the plums and marinating juices, cover and cook for about 15 to 20 mins or until the pork is a very light pink in the center. Take the pork out to cut. Add the mustard to the pork plum sauce to finish. Can be served as a dipping sauce or spooned over the meat.